1. Field of the Invention
This disclosure relates to systems and methods for the use of an underground limestone mine in the treatment of effluent gas from an industrial operation.
2. Description of the Related Art
Flue gas treatment has become a focus of electric utilities and industrial operations due to increasingly tighter air quality standards. As companies seek to comply with air quality regulations, the need arises for effective flue gas treatment options. Alkali species based on alkali or alkaline earth metals are common sorbents used to neutralize the acid components of the flue gas. The most common of these alkalis are sodium, calcium, or magnesium-based. A common method of introduction of the sorbents into the gas stream is to use dry sorbent injections.
One commonly used material for the scrubbing of acid gases is hydrated lime. It has been established that hydrated lime can provide a desirable reaction to act as a mitigation agent (due to its favorable reaction with Sulfur Trioxide (SO3)) and hydrated lime systems have been proven successful in many full scale operations. These systems operate continuously to provide utility companies with a dependable, cost-effective means of acid gas control.
At the same time, while lime products can be useful in the elimination of flue gas pollutants, the production of lime, as is true with a variety of industrial processes, can actually serve as a source for pollutants. Specifically, in a variety of industrial processes such as the production of lime, aluminum, steel, or other materials where significant heat is needed, the heat is often generated from the incineration of fuel, such as coal. The gas exiting these smelters and kilns often contains high concentrations of particulate matter as well as the natural by-products of combustion processes, which are essentially the same as those produced from a power plant utilizing the same type of fuel.
In a lime kiln, the gas will generally comprise lime and limestone particles as well as ash particles from the fuel being burned along with various gaseous pollutants including sulfur, nitrogen, carbon oxide, chlorine and mercury compounds. The gas also still contains much of the heat of combustion that was used to calcine the raw material into lime and is in the range of 1200 to 1300 degrees Fahrenheit.
Lime kilns (and other industrial processes for mined products) are often co-located with corresponding mines in order to simplify processing and transportation in the material production. In the case of lime, the underlying mine is generally a mine for limestone and the mine has rarely had all the limestone removed therefrom.
While limestone is commonly obtained from a quarry, the underground mining of limestone can be both economical and necessary in certain areas. This can be for a variety of reasons including regulatory ones and those related to the economy of removing overlaying rock in order to quarry. Underground limestone mines will generally comprise a “room and pillar” construction to provide for sufficient roof support and stability. Thus, a mine which is in use will often have large unused portions where all economical limestone has been removed and miners have moved on to a different area.